The next received 2/3 of the remainder.
That means the youngest received 1/3 of the remainder.
That one third was $6.
If 1/3 = $6, then 2/3= $12
the total money the two younger received $18
The oldest received 7/13
the other two then received 6/13
so 6/13 = $18
18/6 = 3
1/13 = $3
3 * 13 = $39